Apparatus for working materials with a beam of charged particles



Nov. 1,1966 H. SPRUCK 3,283,120

APPARATUS FOR WORKING MATERIALS WITH A BEAM OF CHARGED PARTICLES FiledMarch 20, 1964 2 Sheets-Sheet 1 HTTOE/VEY Nov. 1, 1966 H. SPRUCKAPPARATUS FOR WORKING MATERIALS WITH A BEAM OF CHARGED PARTICLES 2Sheets-Sheet 2 Filed March 20, 1964 F/GZ F/io

Wl/l/ Ill/4? mmmm H51 M07 JPPUCK 5y a UM Mi HTTflE/VEV United StatesPatent 8 Claims. or. 219-121 This invention relates to working amaterial with a beam of charged particles, and particularly toperforming operations such as welding, cutting, melting, evaporating, ormachining on any material with an electron beam.

In prior art apparatus which are used to work materials with a beam ofcharged particles, the beam of charged particles is focused by means ofan electromagnetic lens on the workpiece to be treated. For thispurpose, the current which flows through the focusing lens is adjustedmanually while the area of the workpiece on which the electron beamimpinges is being watched through an observation device. The lenscurrent which flows through the focusing coil is usually so adjustedthat th impingement point of the electron beam has its narrowestcross-section on the surface of the workpiece.

Such an adjustment of the focusing of the beam is inconvenient and timeconsuming and is, furthermore, inherently affected with subjectiveerrors. If during the Working operation the accelerating voltage or thebeam current set at the beginning of the working operation is changeddue to a variation in the thickness or composition of the workpiece, thefocusing of the beam changes also and therefore it is necessary, whileconstantly observing the impingement point of the beam, to manuallyre-adjust the lens current passing through the focusing lens. Thisnecessity of re-adjusting the focusing action arises also when thesurface of the workpiece treated has a relief-type shape. In this casethere occurs a change in the working distance, i.e. the distance betweenthe lower edge of the focusing lens and the surface of the workpiece.Such a change of the working distance requires a re-adjustment of thefocusing of the electron beam.

As may be seen easily, constant observation of the workpiece coupledwith a constant control of the focusing of the beam is fatiguing andtiresome to the operator of the apparatus.

It has already been proposed to carry out the focusing of the electronbeam automatically. In the prior art, the refractive power of thefocusing lens is varied periodically and the quantity of the chargedparticles coming from the workpiece is measured. As soon as thisquantity reaches an extreme value the magnitude of the'current whichflows at this moment through the focusing lens is held constant. Thismethod can not be continuously practised during the entire workingoperation but it is repeated at periodic intervals during the workingoperation. Furthermore only a relatively small variation of the focusingof the beam may be registered during this process.

The present invention relates to a process for treating a workpiece bymeans of a beam of charged particles focused on the workpiece by anelectromagnetic lens and is characterized particularly in that theproper focusing of the electron beam is constantly maintainedindependently of changes in machine adjustments and working distance.The present invention is based on the observation that during theWorking of the materials by means of an electron beam first theaccelerating voltage, the beam current and the working speed are set,and that during the course of the working operation in most instancesonly the working distance. will change. According to the new PatentedNov. 1, 1966 process the current which flows through the focusing lensis initially automatically adjusted in relation to the values of theaccelerating voltage, the beam current and the working distance to thevalue required for the focusing of the electron beam, and the workingdistance is constantly measured during the working operation and thecurrent flowing through the focusing lens is adjusted in relation tothis measurement.

In this novel process it is therefore necessary to ad just for exampleby means of two control knobs the values of the accelerating voltage andthe beam current determined on the basis of the properties of theworkpiece before the actual start of the working operation. Furthermorethe predetermined working distance is set at a special setting knob.Together with these settings the device for generating the currentflowing through the focusing lens is influenced in such a manner that itsupplies a lens current set to the proper value, that is to say, whenthe operation begins the electron beam is focused on the surface of theworkpiece. If during the working operation a change of the workingdistance occurs, this change is registered constantly and simultaneouslythe current flowing through the focusing lens is constantly re-adjustedin such a way that the proper focusing of the beam is maintained.

It is advantageous to carry out the measuring of the working distance byoptical means. In this case the measurement of the working distance isobtained continuously and automatically and the measured values regulateautomatically the current flowing through the focusing lens.

An optical measurement of the Working distance presupposes that theelectron beam is in operation and that accordingly its impingement pointis brightly illuminated with respect to the dark surrounding area.

The adjustment of the working distance before the start of the workingoperation is obtained by an adjustment to the approximate value, thisvalue being obtained from the known distance between the workpiecesupport and the lower edge of the lens and the thickness of theworkpiece.

After starting the apparatus the proper value of the working distance isthen measured automatically and the lens current supply device isautomatically so influenced that the focusing of the beam is correctlyadjusted.

It is also possible to arrange a tungsten strip at the level of theworkpiece surface, to operate the beam and to measure the bright spotproduced on the strip. In this manner the focusing of the electron beamwhich is correct for the measured working distance is assured. Afterdisconnecting the beam the tungsten strip may be re placed by theworkpiece and thus the beam is focused correctly on the workpiecesurface at the beginning of the working operation.

Under certain conditions it is also possible to produce before the startof the Working operation by means of a regular flashlight a light spoton the workpiece surface and to measure this light spot with the opticaldistance meter. In this manner it is obtained that already at the momentof starting the apparatus the exactly correct working distance is set.

The arrangement according to the invention consists of a known apparatusfor working materials by means of an electron beam which is providedwith an electromagnetic lens for focusing the electron beam. A lenscurrent supply device is provided for the purpose of supplying currentto the focusing lens. Means for determining the magnitude of the lenscurrent are connected to means for adjusting the accelerating voltageand the beam current. Furthermore an optical distance meter formeasuring the working distance is provided, this distance meter beingalso connected to the lens current determining device.

In many cases it is necessary to set the focusing point of the electronbeam in such a way that it does not lie exactly on the workpiece surfacebut so that it lies a certain distance above or below this surface. As anovel feature of this invention, a control member is connected to thelens current supply device for the purpose of adjusting the axialposition of the focusing point. By means of this control member theaxial position of the focusing point may be displaced as desired withoutinfluencing the remaining automatic adjustment of the focusing point inany manner.

The optical distance meter is preferably so designed that it measuresthe bright spot produced by the electron beam on the workpiece andgenerates in the plane of a photocell two pictures of this spot whichcoincide to form a double image upon reaching the balanced state. In thephotocell plane, tWo photocells are provided Whose separation linecoincides with the center line of the double image. These photocells areconnected to a readjusting device which brings the distance meter alwaysinto the balanced position.

The invention will be explained hereafter in greater detail by means ofan embodiment illustrated in the accompanying drawings in which likereference numerals refer to like elements in the various figures and inwhich:

FIGURE 1 shows diagrammatically an embodiment of the apparatus accordingto the invention.

FIGURE 2 shows diagrammatically an embodiment of the lens current supplydevice incorporated in FIGURE 1.

FIGURE 3 shows a partial section of another embodiment of the apparatusaccording to the invention.

The apparatus for working materials by means of an electron beamillustrated in FIGURE 1 shows the cathode 1, the control cylinder 2 andthe grounded anode 3 of the beam generating system. In device 4 a highvoltage of about 100 kv. is generated and supplied by means of a highvoltage cable to device 5. This device is adapted to produce theadjustable heating voltage and the adjustable control cylinder biasvoltage. These voltages are conducted over a high voltage cable to thebeam generator system 1, 2, 3.

A control member 6 is connected to device 4 and is adapted to adjust thevalue of the high voltage. Another control member 7 is connected todevice and is adapted to adjust the control cylinder bias voltage andthus the adjustment of the beam current.

Below anode 3 viewed in the direction of the beam a magnetic deflectingsystem 8 is mounted which is adapted to adjust the electron beam 10.Deflection voltage generator 9 feeds current to the deflecting system 8.

Below the deflecting system 8 a screen 11 is mounted which may be movedby means of knobs 12 and 13 in the plane of the drawing and alsoperpendicularly to the plane of the drawing. After the adjustment of theelectron beam it passes through the screen 11 and is focused by means ofthe electromagnetic lens 14 on the workpiece 16 arranged in the workchamber 15.

An electromagnetic deflecting system 17 arranged be low the focusinglens 14 is supplied with current from lens current generator 18 and isadapted to deflect the electron beam 10 relative to the workpiece 16.

The workpiece 16 is placed in work chamber on a cross-table 19 which maybe moved by means of hand wheels 20 and 21 in the plane of the drawingand perpendicularly to the plane of the drawing. In place of hand wheels20 and 21 electric motors may be provided which carry out the movementof the workpiece 16.

Above the electromagnetic lens 14 an optical lens 22 is mounted which ismovable in the direction of its optical axis. This lens is provided witha bore into which a tube 23 is placed. Electron beam 10 passes throughthis tube 23. The lens 22 is moved in the axial direction by means of anelectric motor 24 and a drive 25. Above lens 22 a mirror 26 is mountedwhich has an opening allowing the passing of the electron beam 10. Theelectron beam 19 generates on the surface of the workpiece 16 a brightlyilluminated spot. The light emitted from this spot passes through lens22 and is projected over the mirror 26 to a pair of photocells 27 and28. Between the mirror 26 and the photocells 27, 28 an additional lens29 is mounted which produces in the balanced state a coinciding doubleimage of the illuminated spot on the workpiece 16 in the plane of thephotocells 27, 28. In a beam portion of the light reflected by mirror 26a filter element 30 is mounted.

Behind the photocells 27, 28 a bridge connection 31 is provided which isconnected to the electric motor 24. The electric motor 24 provides theaxial displacement of the lens 22 and also the actuation of the controlmember 32.

The control member 32 and the two control members 6 and 7 are connectedto a lens current supply device 33. This device furnishes the currentflowing through the focusing lens 14. Additional control member 34 isconnected to the lens current supply device 33 and is adapted to adjustthe axial position of the focusing point of the electron beam 10.

The lens current supply device 33 is illustrated diagrammatically inFIGURE 2. It consists essentially of the potentiometers 35, 36 and 37and of the battery or power supply 38. To adjust the lens current thesliders 39, and 41 are moved. It is also possible .to rotate thepotentiometer 37 relative to its slider 41 and this is irzme by means ofthe control knob 34 via driving gears The operation of the apparatus isas follows: Before starting the working operation and based on theproperties of the workpiece the accelerating voltage is set by means ofcontrol 6 and the beam current by means of bias voltage control 7. Bymeans of control 6 the slider 39 and by means of control 7 the slider 40are moved in the lens current supply device 33. The work distance isthereafter set by means of control 32 whereby slider 41 is moved. Thecontrols 6, 7, 32 and 34 co-operate with dials not shown in the drawing.After controls 6, 7 and 32 are set such a resistance value isestablished across potentiometers 35, 36 and 37 that the lens currentsupplied from source 33 to focusing lens 14 produces a focusing of theelectron beam 10 on the surface of the workpiece 16.

When the working distance changes after the electron beam 10 has beenoperated, the optical arrangements 22, 26, 29 produces in the plane ofthe photocells 27, 28 no coinciding double image of the illuminated spoton the workpiece 16. The two images deviate from the center by oppositeequal amounts. By means of filter 30 it is obtained that one of thephotocells 27, 28 receives less light than the other cell. Due to this,the bridge 31 becomes unbalanced and the electric motor 24 receivescurrent. This moves lens 22 over drive 25 in the axial direction until,in the plane of the photocells 27, 28, a coinciding double image isreestablished. This movement of the lens 22 is simultaneouslytransferred over control 32 into the lens current supply device 33. Theslider 41 on potentiometer 37 is thereby displaced and the currentthrough focusing lens 14 is varied in a direction which refocuses theelectron beam at the surface of the workpiece 16 in spite of the changedworking distance.

In the case where the focusing point of the electron beam 10 lies aboveor below the surface of the workpiece 16 this displacement is fed intothe lens current supply device 33 by means of the control 34. By meansof con trol 34 the potentiometer 37 is rotated as a whole over drive 42relative to slider 41. Thus the current flowing thnough the focusinglens 14 is changed to a small extent and this change causes adisplacement of the axial position of the focusing point.

In the example illustrated in FIGURE 3 an optical distance meter isarranged in the work chamber 15 below the focusing lens 14. Thisdistance meter consists of mirrors 50 and 52 and lenses 54 and 56. isdesigned to be semi-transparent.

The distance meter is so .set that it produces, in the balancedposition, in the plane of two photocells 58, 60 a coinciding doubleimage of the illuminated spot on the workpiece 16. If the workingdistance changes a coinciding double image is no longer created in theplane of the cells 58, 6t) and the two partial images deviate from eachother. Due to this, one of the two photocells 58, 60 receives morecurrent than the other cell and the associated bridge connection 62starts to operate. Over this bridge connection the electric motor 64receives current and this motor rotates over the flexible shaft 66 themirror 52 until in the plane of the photocells 58, 60 again a coincidingdouble image is obtained. Simultaneously with the rotation of the mirror52 the control 32 of the lens current supply device 33 is actuated. Theelectron beam may impinge continuously on the workpiece 16. However, inmany cases it is advantageous to select instead of a continuouslyimpinging beam a beam which is effective in a pulsating manner. Thispulse-like effect of the beam does not disturb the optical distancemeasurement because the impulses are kept so short that no change occursin the illuminated spot on the surface of the workpiece 16.

The present invention is particularly suitable for application inapparatus for milling, cutting, soldering or welding by means of anelectron beam. In all these cases the workpiece is moved continuouslyrelative to the electron beam so that upon a change in the workingdistance a continuous readjustment of the focusing action is necessary.The present invention finds also appropriate application in apparatusfor drilling by means of an electron beam. If in such applicationsseveral holes are to be drilled in a workpiece at different locations itis not necessary to re-adjust manually the focusing action between thediiferent holes because also in this case an automatic re-adjustmenttakes place.

What is claimed is: 1. Apparatus for working material with an energizedbeam comprising:

means for generating an energized beam, means for focusing said beam ata material to be worked,

means for optically measuring the working distance between said focusingmeans and the material to be worked and for generating a signalindicative of a variation in said working distance from a desired value,and

means responsive to said signal indicative of a variation in workingdistance for controlling said focusing means whereby said beam ismaintained focused at the material to be worked.

2. The apparatus of claim 1 wherein said means for generating anenergized beam comprises:

a source of charged particles,

The mirror 52 means for accelerating the charged particles from saidsource toward a material to be worked, means for forming saidaccelerated particles into a beam, and means for controlling the beamcurrent. 3. The apparatus of claim 2 wherein said focusing meanscomprises:

an electromagnetic lens for focusing the beam of charged particles. 4.The apparatus of claim 3 wherein saidmeans for controlling the focusingmeans comprises:

an adjustable lens current supply, and means responsive to said signalindicative of a variation in working distance for varying the currentflowing from said supply through said electromagnetic lens. 5. Theapparatus of claim 4 further comprising: means coupling said particleaccelerating and beam current controlling means to said lens currentsupply whereby adjustment of the beam current or particle accelerationvaries the lens current. 6. The apparatus of claim 5 wherein saidoptical working distance measuring means comprises:

mean for sensing the illuminated spot produced on the material beingworked by the beam and for producing two images thereof, and lightsensitive means responsive to the images produced by said sensing meansfor generating an electrical signal indicative of a variation in workingdistance when said images do not coincide. 7. The apparatus of claim 6wherein said sensing means comprises:

optical system having a variable focal length, means responsive to thesignal generated by said light sensitive means for varying the focus ofsaid optical system, and an optical filter positioned between saidoptical system and said sensing means for attenuating one of saidimages. 8. The apparatus of claim 7 wherein said light sensitive meanscomprises:

two photocells whose separation line coincides with the center line ofthe coinciding images, and means connecting said plhotocells as legs ofa bridge circuit whereby an electrical output signal in generatedwhenever the images do not coincide.

References Cited by the Examiner UNITED STATES PATENTS 2,304,814 12/1942Glasser 88l 2,472,951 6/1949 Klinke 318480 X 2,945,132 7/1960 Schuoh250222 X 3,037,423 6/1962 Shurclifl? 881 3,158,733 11/1964 Sibley219-121 X JOSEPH V. TRUHE, Primaly Examiner.

1. APPARATUS FOR WORKING MATERIAL WITH AN ENERGIZED BEAM COMPRISING:MEANS FOR GENERATING AN ENERIGIZED BEAM, MEANS FOR FOCUSING SAID BEAM ATA MATERIAL TO BE WORKED, MEANS FOR OPTICALLY MEASURING THE WORKINGDISTANCE BETWEEN SAID FOCUSING MEANS AND THE MATERIAL TO BE WORKED ANDFOR GENERATING A SIGNAL INDICATIVE OF A VARIATION IN SAID WORKINGDISTANCE FROM A DESIRED VALUE, AND MEANS RESPONSIVE TO SAID SIGNALINDICATIVE OF A VARIATION IN WORKING DISTANCE FOR CONTROLLING SAIDFOCUSING MEANS WHEREBY SAID BEAM IS MAINTAINED FOCUSED AT THE MATERIALTO BE WORKED.